1. Field of the Invention
The present invention relates to a metal bonded structure and a metal bonding method. More specifically, the present invention relates to a copper-copper bonded structure and a copper-copper bonding method.
2. Description of the Related Art
As an electrically conductive material used to form a wiring layer that is a component of a wiring substrate, or used to form an electrode surface of each electrode of a semiconductor chip or the like, copper is widely employed. As a conventional metal bonding method for electrically connecting a first bonding member to be bonded such as a wiring layer of a wiring substrate or the like to a second bonding member to be bonded such as an element electrode of a semiconductor chip, examples of such a conventional metal bonding methods include: a method in which the bonding faces are solder-bonded via solder; a method in which the bonding faces are bonded to each other by applying pressure while heating the bonding faces at a high temperature; and a method in which the bonding faces are activated by means of ion irradiation or the like in a vacuum so as to bond the bonding faces to each other; and so forth.
[Related Art Documents]
[Patent Documents]
[Patent Document 1]
Japanese Patent Application Laid Open No. 2003-100811
With such a method in which a copper member is bonded to another copper member via solder, a Cu—Sn alloy layer occurs at a bonded interface between each copper layer and the adjacent solder layer. Such a Cu—Sn alloy layer has relatively large electric resistance, and poor ductility, leading to a problem of poor electrical characteristics and/or a problem of poor connection reliability at such a bonded portion. With such a method in which the bonding faces are bonded to each other by applying pressure while heating the bonding faces at a high temperature, in some cases, such an arrangement leads to a problem of damage of the wiring substrate or the semiconductor chip due to the application of heat or the application of pressure. With such a method in which the bonding faces are activated in a vacuum so as to bond the bonding faces to each other, such an arrangement requires large-scale equipment such as a vacuum apparatus, leading to an unavoidable increase in costs.